As shown in FIG. 8, a main guide tape 12 and a branch guide tape 13 configured by magnetic tapes are laid down along a path on which a magnetically guided unmanned conveyance vehicle 11 travels. The main guide tape 12 guides the unmanned conveyance vehicle 11 onto a main travel track, and the branch guide tape 13 guides the unmanned conveyance vehicle 11 onto a branch travel track. A plurality of magnetic markers 14 for providing various operation instructions (control information) of, for example, a turn, a stop, an acceleration, and a deceleration to the unmanned conveyance vehicle 11 are arranged on the left and right sides of the main guide tape 12. The magnetic markers 14 are also configured by magnetic tapes. The unmanned conveyance vehicle 11 includes a guide sensor 61 configured by a large number of Hall elements 61a for detecting the main guide tape 12 and marker sensors 62 and 63 for detecting the magnetic marker 14. In FIG. 8, an arrow extending along the main guide tape 12 represents a forward travel direction of the unmanned conveyance vehicle 11. An arrow extending in a lateral direction represents the right direction of the unmanned conveyance vehicle 11 in the travel direction.
A control unit (not shown) of the unmanned conveyance vehicle 11 calculates a deviation Δ between the center position O1 of the main guide tape 12 detected by the Hall elements 61a of the guide sensor 61 and the center position O2 of the guide sensor 61, i.e., the vehicle body. The control unit controls a drive device of the unmanned conveyance vehicle 11 such that the deviation Δ becomes zero. In this manner, the unmanned conveyance vehicle 11 is unmanned-guided along the main guide tape 12. When magnetic markers 14 are sequentially detected by the marker sensors 62 and 63 while the unmanned conveyance vehicle 11 travels, the control unit controls the drive device to perform, in the order of detection of the magnetic markers 14, a speed change registered in advance or a course change to the branch guide tape 13 as shown in FIG. 8 (see Patent Document 1).
The magnetic forces of the magnetic tapes configuring the guide tapes 12 and 13 and the magnetic markers 14 are in proportion to the sizes of the tapes. For this reason, the magnetic flux density above the magnetic marker 14 that is cut short is smaller than the magnetic flux densities of the guide tapes 12 and 13, as shown in FIG. 9. For this reason, the marker sensors 62 and 63 require detection accuracy higher than that of the guide sensor 61 in order to eliminate erroneous detection.
In order to solve the above problem, the present applicant has proposed the following magnetic marker detecting device. The magnetic marker detecting device is configured such that, as shown in FIG. 10, a magnetic member 64 is arranged near and above the guide sensor 61 and the marker sensors 62 and 63. The magnetic member 64 is made of iron and has a horizontally long quadratic prismatic shape. The magnetic flux output from the main guide tape 12 is guided to the magnetic member 64, and the magnetic flux is induced from the magnetic member 64 to the magnetic marker 14. In this manner, a new magnetic flux flow 65 is generated. The magnetic flux induction causes strong magnetic fluxes to act on the guide sensor 61 and the marker sensors 62 and 63. This results in an improvement of the detection sensitivity of the main guide tape 12 by the guide sensor 61 and the detection sensitivities of the magnetic markers 14 by the marker sensors 62 and 63 (see Non-patent Document 1).